Softening rubber



Patented Aug. 5, 1952 UNITED STATES PATENT OFFICE SOFTENING RUBBER Tracy M. Patrick, Jr., Dayton, Ohio, assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Application July 19, 195 0;,"

Serial No. 174,783

16 Claims. (Cl. Zak-36.2)

This invention relates to softeners for rubbers and deals more particularly with methods of softening or plasticizing natural rubbers or synthetic rubbers su h as thfpoiyrriersand co polymers f 1,3-butadien compounds. In the manufacture of rubber goods, there is commonly added to the rubber, during processing, a material which softens, i. e., decreases the flowresistance of the rubber and thereby facilitates processing operations such; as rnilling, calenderins, extruding, molding: etc. These operations are particularly difficult when working with synthetic rubbers, and numerous materials have been investigated as possible softeners for synthetic rubbers. Such prior materials have been gen- 'erallyof limited usefulness, inthat the improvement of workability of the rubbers was often ob-' tained only at the expense or adversely affecting the properties of the finished products, e. g., strength, odor, etc. Also, while a number of softeners were found to increase the plasticity of the rubbers during some of the'processing steps, their plasticizing action was often destroyed in other processing steps so that the final extruded or molded rubbers were brittle and useless.

Now I have found that certain thiophene derivatives not only effect decreased flow-resistance of the rubberdur-ing processing, but-also serve as plasticizers to yield a final product which has been permanently modified with respect to plasticity, flexibility, strength and other physical and mechanical properties.

The thiophene derivatives which I employ to obtain the improved; rubber's'icomprise phenyl hydrazones of :an aldehyde containing a thiophene nucleus and selected from the class consisting of ph'enylhydrazone's or ,2-thiophenecarboxaldehyde, 3-thiophenecarboxaldehyde, 2- thianaphthenecarboxaldehyde and B thianaph thenecarboxaldehyde and derivatives of such aldehydes in which atleast one nuclear hydros gen hasbeen substituted by a m mber of the grou consisting of' chlorine, bromine and alkyl radicals of from 1 to 4 carbon atoms; .7

1 One class of thiophene derivativeswhichlhave found to be particularly useful forj'th presentmula in which member of the group consisting of hydm en, -chlorinepbromine and:alkyl radi- 5 purpose comprises the thiophenecarboxaldehydes1 and derivatives thereof having tnig'enerai for v in which R is a member and in which one X must be R and the other X must be Gornpounds having the above general formula may be illustrated by the phenylhydrazones of 2- thiophenecarboxaldehyde, 5-chloro-2-thiophene- .carboxaldehyde; methyl 2 7 thiophenecarboxaldehyde, i ,5 dimethyl 2 -thiophenecarbo raldeh e, r t Y e hen car s e s vde. 5 npropyl-2-thiophenecarboxaldehyde, 3thiophenecarboxaldehyde, 2-chloro-3-thiophenecarboxalde hyde, 2-bromo-3-thiophenecarboxaldehyde, etc.

Another class of'co'mpounds which may be employed as plasticizers to ,yieldimproved rubber compositions according to the present invention com-prises the thianaphthene derivatives having the general formula ,t of the class consisting of hydrogen, chlorine, bromine and alkyl radicals of from 1 to 4 carbonatoms and X is a member of the class consisting of R and the radical (E'=NN- CaH5 I and in which one X must be R and the other X must be 'theflphenylhydrazones of Z-thiophenecarboxaldehyde may be readily prepared by treating thiophene with N-methylformanilide in th presence of phosphoryl chloride, steam-distilling the resulting complex. to obtain 2-thiophenecarboxal' ,dehyd e and reacting the latter with phenylhydrazine.

The present thiophene derivatives, as is. customary with rub er; plas'ticiir's,'areipfeferably mixed into the rupperprevmssite or "during the milling operation. However, they maybe added at any stag or the rubber processing to. yield nnished products of improved physical characteristics; The amount of the present. softeners or plasticizers employed depend's upon the nature of the rubber with'which itis to be used as Well as the" degree or oftening esir d'aii'd' genera-11 '60 ranges from; say, about 0.5 part to 5.0 partsor r ,7 3 more per 100 parts of the rubber. The usual compounding ingredients, e. g., materials ,such as sulfur, zinc oxide. antioxidants; fillers, etc., are added at appropriate operating steps in customarily employed quantities.

The term rubber as herein employed refers generally to natural rubber and synthetic rubbers i I such as those obtained by polymerizing a 1,3- 7' butadiene compound either alone or in'admixture with other polymerizable compounds which are capable of copolymerizing with the LS-butadiene compounds. Examples of 1,3-buta'diene compounds which yield synthetic rubbers by'polymerization or copolymerization are 1,3-butadiene.

tion. Specimens were heated for 10 minutes at a temperature of 163 C. and viscosities and plasticities were determined .on both the unheated and heated samples. The technique employed for the Mooney viscosity tests was that described in the American Society for Testing Materials. Specification D927-47T. The plasticity determinations were made by the Williams (Parallel 'Plate) technique (American Society for Testing Materials, Specification D926-47T) and the Firestone technique (noting the time required to 'extrude 5 cc. of-the specimen at p. s. i. at

The following results were obtained:

. Peioent softener Mooney Viscosity Firestone Ifl asticity Williams Plasticity Based on Weight v Rubber .Ufnheated Heated Unheated Heated Unheated Heated 32 T32 19 11 147 13a 45 4a 11 180 use 41 44 20 14 195 20a 60 so 31 257 266 Ez cmple z chloroprene, piperylene," 2,3-dimethyl-1,3 buta- 'diene, etc. As illustrative-of compounds capable of "copolymerizing' with such -1,3-butadienes are compounds which contain a Example 1 v The softening effect of z-thiophenecarboxaldehyde phenylhydrazone on low temperature The softened rubber stock of Example 1 was compounded as follows:

. Parts by weight Low temperature GR-S rubber softened with 2-thiophenecarboxaldehyde phenylhydrazone 100.0 Philblack O '(a'commercially available carbon black) 50.0 Zinc oxide 5.0 Paraflux (an asphaltic'fiu'xi"; 8.0 Santocure (N cyclohexyl 4 2-benzothiazyl sulfenamide accelerator) 1.2

Homogeneous compositions were formed which gave smooth sheets from mill rolls. Vibration properties of the cured, compounded stock were tested and compared with similarly compounded stocks containing other plasticizers by means of a Goodrich Flexometer at 175 p. s. i., 0.175 inch and 30 strokes per second. The following re- GR-S rubber (a commercially avallable butasults were obtained:

Change I Y r"- H'a. ure c e nen Plasticlzer in Soitened GR S Stock During set. lilac,

- 142C. pression Flexure, Percent p Percent 3% of 2-thiopl1enecarboxaldehyde phenylhydrazone- 45 20. 0 7. 5 14. 2 73 3% of 2-thiophenecarboxaldehyde phenylhydrazone i 28. 0 7. 0 11. 8 68 v of Z-thwphenecerboxsldehyde v phenylhydrazone 45 ,'28.4 9.0 14.8 2% of 2-th1ophenemrboxaldehyde phenylhydrazone 60 28. l 6. 5 11. 6 70 1% or Z-thiophenecsrboxaldehyde phenylhydrazone 45 27.3 v 9.6 15.7 73

1% of 2-thlophenecarboxaldehyde phenylhydrazone 60 25. 8 5. 2 12. 2 70 1% of plast cizer A 45 25. 7 l0. 0 16. 6 78 1% of'plast cizer A 60 24. 7 6. 7 13. 0 72 1% of plastrcizer B I 45 27. 6 14. 8 19. 5 1% of plasticizer B 60 27.3 10.8 15.4 80

-' 13 Commercially available rubber plasticizers. diene-styrene copolymer) was evaluated by em ploying the following procedure: I

The rubber was banded to a 6 inch x 12 inch laboratory rubber mill having its 'rolls heated to approximately C. Mixing was initiated and the softener, in the amounts indicated below, was added after a time of 30 seconds. The mixing was continued for an additional 6 minutes. A portion of the mixed batch was then cut off and sheeted for test'specimens prepara The vibration properties of compounded, lowtemperature GR-S stocks containing 2-thiophenecarboxaldehyde phenylhydrazone, as shown in the above table, are superior to those obtained 70 when using the known rubber plasticizers.

The invention is not limited to the "specific embodiments herein disclosed. The preferred phenylhydrazones may be employed in diflerent proportions than specifically shown and in conjunction with other compounding and vulcanicing ingredients, qbv-iouslm many variations om c A group and is copolymerizable with th 1,3'-butadiene compound, and, as a softener therefor, a

phenylhydrazone of an aldehyde selected from the class consisting of 2-thiophenecarboxaldehyde, 3-thiophenecarboxaldehyde, 3-thianaphthenecarboxaldehyde, 2 -}thianaphthenecarboxaldehyde and derivatives :or

least one nuclear hydrogen has been replaced by a member of the group consisting of chlorine, bromine and alkyl radicals of from 1 to 4 carbon atoms.

2. A composition of matter comprising a synthetic rubber copolymer of 1,3-butadiene and styrene, and, as a softener therefor, a phenylhydrazone of an aldehyde selected from the class consisting of 2-thiophenecarboxaldehyde, 3- thiophenecarboxaldehyde, 3 thianaphthenecarboxaldehyde, 2 thianaphthenecarboxaldehyde and derivatives-of the same in which at least one nuclear hydrogen has been replaced by a the same in which at member of the group consisting of chlorine, bromine and alkyl radicals of from 1 to 4 carbon atoms. J

3. A composition of matter comprising a rubber selected from the class consisting of natural rubber, polymeric l,3-butadiene compounds and co olymers of 1,3-butadienecompoundswith a compound which contains-a v group and is copolymerizable with the 1,3-butadiene compound, and, as a softener therefor, a thiophene derivative having the gene'ralformula in which vR, is a member of; the group consisting of hydrogen, chlorine, bromine and alkyl radicals of from 1 to 4 carbon atoms-and Xisa member of the class. consisting of R and the radical a i J -"'O=N N OQH5 and in which one X must be R andpthe other mustbe s a '--?=NN"CtH5 diene compound," and, "as 'as'often'e'r tnerrcrf a "(5 which R is a member' pffthe classconsisting of hydrogen, chloj 'in'e; bromine: and alkylra'di'cals of from 1; to "4 carbcn atoms and is amember of the class; consistin'gfbf B and the radical e -n tr te; s

and inwhich one X must be Randal-1e "other K ere! ;:I j N- fiiflgf 5. A composition of matter comprism asynthetic 'rubloer copol'yme'r *o'f 1-,3-butadiene "and styrene, and; as a softener-therefor, a thi'ophene derivative having the general formula f BC 0 in which R is a member vii-the group consisting of hydrogen, chlorine,bromine and" alkyl radicalsjof from 1 to f4 "carbon'atoms and X is a member of the class consisting or R 'andthe radical C=N--I I--CHs 6. A composition of matter comprising a synthetic rubber copolymer of 1,3-butadiene and styrene and, as a softener therefor, a thianaphth'ene derivative having the general formula .s

I ofthe class-consisting of hydrogen, chlorine. bromine and alkyl radicals of from 1 to 4 carbon atoms and X is a member of the class consisting of R and the radical -in-which R is a member and in which one'X'mnst-"be R-and the other'X tr '11,

C=N-.N-C6H5 7. A composition of matter comprising a synt c; ,grub e ii QQ IWQF'OIY L'a-b d n styrene'anwthephefiylh mzoiie'of'2 -thioph'enacarboxaldehyde as a softener'there'for;

8. A composition of matter'comprisinga 'synthetic rubber copolymer of- 1,3-butadiene and acemes group and is copolymerizable with the 1,3-butadiene compound which comprises incorporating therein a phenylhydrazone of an aldehyde selected from the class consistingot Z-thiopheneicarboxaldehyde, af thiophenecarboxaldehyle 3- .tmene iithenee rbbxldehi'deg Z thianaphthenecanboxa1dehyde}andderiyatiyes er the same in which at least one nuclear'hydrogen has been replaced by a memberof the group consisting of chlorine, bromine andalkyl. radicals of from 1 W c r q a o s; f .i it. i

10. The method of plasticizing a synthetic rub ber copolymer of 1,3-butadiene and styrene which comprises incorporating therein a, phenylhydrazone of an aldehyde selected from the class consisting of 2 j; thiophenecarboxaldehyde, -3 i-thiophenecanboxaldehyde, 2 thianaphthenecarboxaldehyde, and 3- thianaphthenecarboxaldehyde and derivatives of the same in which at least one nuclear hydrogen has been replaced by a member of the group consisting of chlorine, bromine and alkyl radicals of from 1 to 4 carbon atoms.

11. The method of plasticizing a rubber selected from the: class consisting. of natural rubber, polymericlB-butadiene compounds and copolymers otl,3 b'utadiene compounds with a compound which contains a h .group and is copolymerizable with the 1,3- butadiene "compound which comprises incorporating therein a thiophene derivative having the eneral formula Rc'-cx in which R is a-member of the group consisting of hydrogen, chlorine, bromine and alkyl radicals of from 1 to 4 carbon atoms and X is a member of the class consisting'oi" R and the radical 'and'yinwhichlone "be-R and the other X butadiene compounds which comprisesincor'porating-therein.af me epfhti ep der vative hav a w i m WQ QWP QWA of from i to 4 carbon atoms and X is a member of the class consisting of R and the radical and in which only one X must R andthe other -X'mustbe r e 'Ci= N N CcHs 13. The method of plasticizing a synthetic rubber copolymer of LB-butadiene and styrene which comprises incorporating therein a thiophene derivative having the general formula member of the class consisting oi R and the radical. j

I (Ij=N- CQH! and inwhich one-X must be R and the other x must be 1 a 4 i I CII=N I Co s 14.' The method of plasticizing a synthetic rubber copolymer of 1,3-butadiene and styrene which comprises incorporating therein a thianaphethene .deriyative havingthe general formula ox EX 7 L \S/ a in which R is a member or the group consisting of hydrogen, chlorine, bromine and alkyl radicals of from 1 to 4 carbon atoms and X is a member 01' the class consisting of R and the radical -(l3=N-NCeH and in: which one X must be R and the other X must be a g l5. The method of plasticizing a synthetic rubber copclymer of l-,3 -butadiene and styrene which comprises 1 incorporating therein the phenylhy- Ypart to 5.0 partsiper parts by weight of said b bnsr uieee. pp;

copolymer.

TRACY M. PATRICK, JR.

REFERENCES CITED The following references are of record in the m ei m iee ee I Organic Chemistry" by P. Karrer (2d ed.),

737, 73 8and 743. 

1. A COMPOSITION OF MATTER COMPRISING A RUBBER SELECTED FROM THE GROUP CONSISTING OF NATURAL RUBBER, POLYMERIC 1,3-BUTADIENE COMPOUNDS AND COPOLYMERS OF 1,3-BUTADIENE COMPOUNDS WITH A COMPOUND WHICH CONTAINS A 